1. Do not use an apostrophe with nouns that are not possessive. ... Do not use an apostrophe in the possessive pronouns its, whose, his, hers, ours, yours, and theirs.

Is it their's or theirs?

The Bottom Line

The idea that theirs needs an apostrophe comes out of the fact that on virtually every other word, 's indicates possession, so English speakers sometimes think theirs should be spelled their's. However, this is always incorrect – theirs is the only correct spelling.

What is difference between their and theirs?

Their is a possessive adjective. It modifies a noun: "their house", "their dogs", etc. Theirs is a possessive pronoun. It is used without a noun: "these books are theirs".